The rescuer tells them: "You are very strong, very strong". "I haven't had anything to eat".
Governor Narongsak added that "the operation isn't over", and the rescue will be completed when all 13 have been brought of out of the flooded cave system safely.
Narongsak said that an operations center has been set up in the third chamber, about 1.7 kilometers (a mile) from entrance to the cave.
Family members of the missing hugged each other as they cheered the news.
Chiang Rai Governor Narongsak Osatanakorn confirmed the group been found but warned they were not yet out of danger and must be strengthened for the arduous job of getting back out again.
The rescue teams have been working against relentless rains that hindered their every move - pumping the water out of a cave system is nearly impossible when it is actively flooding again. We are now planning how to send nurse and doctor inside the cave to check their health and movement.
He said the rescue was underway and that the conditions of the group was being evacuated.
The mother of one of the boys, Aikarn Wiboonrunreung, said: "Today is the best day". So they're being fully immersed in water, wearing what we know is a full face mask or maybe even some sort of commercial dive helmet to make it a little less stressful for them.
"How many of you are there - 13?"
Another player asks when will they get out of the cave.
Prime Minister Prayuth Chan-ocha thanked the worldwide experts and rescuers.
(CBS4) - Twelve boys and their coach alive were found alive Monday, after spending more than a week trapped in a cave in Thailand.
"Thirteen? Brilliant!" the rescuer says, before continuing: "We are coming, it's OK, many people are coming. we are the first".
Mr Narongsak said the passageway the divers made their way through goes upwards in some places and downwards in others and is extremely narrow, making it hard for divers to fit through with all their gear. "They will take care of each other".
Rescue efforts had been repeatedly hampered after the 12 children went missing, due to rising muddy water forcing divers to withdraw.
As part of the rescue effort, search parties have been lowered down shafts on the mountainside, but it was unclear what progress they had made, or exactly where they were in relation to the "Pattaya Beach" chamber.
Thanakorn Ingsilapakul, 15, of Mae Sai Prasitsart school, where six of the missing boys attended, told Reuters he is "really anxious", about his classmate in the cave, "but I am hopeful because my friend is strong".
So far, rescuers have been able to pump excess water from the cave and divert groundwater as well while searching for a safe way to reach the team.
According to news.com.au, the boys likely had access to freshwater - either dripping in though rocks or rushing in through the entrance - but experts warned that run-off water from nearby farms could carry risky chemicals or bacteria.
The captivating search for the group brought in cave rescue experts from the USA military, the UK, China and Australia. The rescue teams spent much of Monday making preparations for what was hoped would be the final push in their search for team.